1. Field of the Invention
The invention relates to brain wave medical systems and methods and more particularly to an electroencephalograph (EEG) Deblurring system and method having improved spatial detail.
2. Description of Related Art
Electroencephalography is a simple noninvasive technique for monitoring brain function based on amplification of brain potentials recorded at the scalp. Although the EEG has been measured for over 65 years, its full potential as a technology for imaging brain function has not yet been realized. Its chief advantages when compared with other brain imaging technologies such as positron emission tomography or functional magnetic resonance imaging are: 1) millisecond-level temporal resolution necessary for resolving sub-second neurological processes; and 2) simplicity of the sensors (essentially a small piece of metal and an operational amplifier) which results in low cost and ability to record for prolonged periods of time in ordinary hospital rooms, at home, or even from ambulatory patients. The chief disadvantage of the traditional EEG method is poor spatial detail. There are two obstacles to substantially improving the detail of EEG recordings. The first is simply that more scalp recording sites are needed. While it is the usual clinical practice to record EEGs from 19 sites, it has been demonstrated with recordings from up to 124 sites that additional spatial information is readily available (Gevins et al, 1991, 1994). The U.S. Pat. No. 4,736,751, incorporated by reference, describes a system using a larger number of electrodes and various digital computer based methods to obtain more information from the brain wave signals. U.S. Pat. Nos. 4,967,038, 5,038,782, 5,119,816 and incorporated by reference, describe systems for conveniently obtaining EEG recordings from a larger number of electrodes and locating their positions.
The second obstacle is that spatial enhancement procedures are needed to reduce blur distortion that occurs as potentials generated in the brain are volume conducted through brain, cerebral spinal fluid, the low-conductivity skull, and scalp to the recording electrodes at the scalp surface. Spatial enhancement is possible since the 3 dB point of the point spread function for conductance of potentials from the brain surface to the scalp averages about 2.5 cm; with 128 electrodes spaced evenly on an average adult head, the interelectrode distance is about 2.25 cm. U.S. patent application Ser. No. 07/868,724 for "EEG Spatial Enhancement Method & System", filed Apr. 14, 1992, now U.S. Pat. No. 5,331,970, issued Jul. 26, 1994 and incorporated herein by reference, describes a system and method, called Deblurring, which improves the spatial detail of the EEG based on measurements of the positions of the electrodes on the subject's head, measurements of the subject's head size, shape, scalp thickness, skull thickness and brain shape, and estimates of the conductivity of the skull, scalp and cerebral spinal fluid. However, the method requires a means of measuring each electrode position, a Magnetic Resonance Image or other means of measuring the subject's head size, shape, scalp thickness, skull thickness and brain shape, a considerable amount of manual effort in order to trace out structures from a subject's Magnetic Resonance Image, as well as a large amount of computation time.